1. Field of the Invention
The present invention relates to semiconductor power switching devices such as power MOSFET devices, and more particularly, to a semiconductor device including molded wireless exposed during packaging and a method of packaging the same.
2. Description of the Prior Art
Semiconductor power switching devices, and particularly, power MOSFET devices, continue to push the lower limits of on-state resistance. While silicon technology has advanced significantly in the past decade, essentially the same decades old package technology continues as the primary packaging means. The epoxy or soldered die attach along with aluminum or gold wire interconnects is still a preferred power device package methodology. Recently, packages have been manufactured by connecting the die within the package to the leads directly through a low resistance solder connection. By using a second leadframe element and solder to connect the package conductors and the first leadframe, a direct connection is enabled. Furthermore, the size and shape of the second leadframe may be tailored to fit the chip device and to minimize its electrical and thermal resistance.
When gold wire bonding is done on a gate connection within a chip, the use of adhesives may introduce resin bleeds that are difficult to control and can interfere with the gate bond contact integrity. When silver-filled adhesives are used on the source and drain connections, since adhesives do not flow selectively, the resulting device is generally more prone to source shorting within the gate or drain. Additionally, adhesives generally have inferior electrical conductivity compared to solders.
Recently, copper straps have been used to couple dies to leads. Generally, with such arrangements, more than 60% of the die area is occupied by the copper strap with adhesives underneath the copper strap. This means less mold plastic is available to securely hold the internal assembly. Since a bigger area is allocated for adhesives, this also means more chances for void formation of the chip device.
Finally, another concern with regard to packaging of semiconductor devices is the elimination of heat generated by the device. Generally, power MOSFET devices can generate a fair amount of heat.